Eyeglasses having exchangeable lenses or lens assemblies offer several advantages over conventional eyeglasses having fixed lenses. For example, in the case of sunglasses, different pairs of lenses can be provided for varying light conditions. Some of these lenses are preferably polarized to protect the eyes against ultraviolet rays. In the case of prescription glasses, lenses manufactured to the current prescription of the wearer can be easily exchanged for the out-of-date prescription lenses. Also, in the case of lens and/or frame damage, a single component can be replaced more economically than purchasing an entirely new pair of eyeglasses.
Exchangeable lens eyeglasses have been known for some time but older designs have had significant shortcomings in that they are generally of complex mechanical structure making them expensive to manufacture. Other designs require substantial mutual deformation of the lens and the front component of the frame making insertion and removal of a lens cumbersome and difficult.
Recently introduced exchangeable eyeglass designs have overcome these shortcomings by making replacement of the lenses convenient. In one structure disclosed in U.S. Pat. No. 4,176,921, the eyeglass front is disclosed as being made of wire with complete rims (rims completely encompassing the lenses). Welded to the wire rims are two spaced lower prongs for supporting each lens. An additional prong extends adjacent the temple piece, and is either integral with the rim, or is secured in another welded joinder. The lenses, which are stored without a frame means until ready for use, are inserted from above until they are embraced by the prongs. A metal lever is hinged to the bridge joining the rims and carries a prong for each lens. The lever is rotated downwardly to a holding position, to prevent upward movement of the lenses. Separate plastic nose pads are attached to the wire front. The eyeglasses shown in this patent have met with widespread success but they are relatively expensive due to the complete wire front, which is typically formed of a wire stock, and must be welded in a separate forming step to form a closed loop. Also, a complete wire rim is limited in its ability to accommodate designer materials and colors.
Complete wire rims, especially those for mating with exchangeable lenses can present a problem in that the wire rims are susceptible to bending or other deformation, which destroys the relatively close-tolerance lens-conforming configuration. Also, the lenses themselves are unsupported during storage. Plastic lenses may tend to warp if stored under conditions of excessive heat or pressure.
An eyeglass configuration for a front assembly having partial rims (rims which extend about the periphery of typically only the upper or lower portion of the lenses) is disclosed in U.S. Pat. No. 4,523,819. The eyeglass front includes wires or threads which are received in grooves in the exposed bottom edges of the lenses. The threads are fastened to one end of their associated partial rim and meet at the bridge section of the front where their remaining ends are held by the free ends of pivotal levers for tensioning the threads. A retainer clip, which is hinged to a lower bridge member, overlies the lever free ends to maintain the levers in their tensioning positions. The front used in the eyeglasses is preferably formed of metal to accommodate the wear occasioned by the use of pivoting components, to permit the attachment of prongs, and to provide adequate strength for tensioning. While generally satisfactory, the eyeglasses shown in this patent present some difficulties for wearers who have limited manual dexterity or who are engaged in outdoor winter sports or other activities requiring gloves.
Another arrangement of an interchangeable eyeglass configuration is shown in U.S. Pat. No. 2,738,709. An eyeglass frame made of wire is provided for mounting two lenses, and includes an intermediate metal bridge portion. The wire frame is adapted to be received behind an overlying plastic frame containing the customary temple pieces for engaging the temples and ears of a wearer. Both the wire frame and the overlying plastic frame have complete rims which completely encircle the lenses. Recesses are provided in the rear of the overlying plastic frame (adjacent the wearer's face), to receive the entire rim portions of the wire frame. Two hingeable latches are provided on the overlying plastic frame adjacent the temple pieces to secure the wire frame thereto.
This interchangeable eyeglass arrangement has considerable mass or bulk and is therefore relatively heavy. The overlying plastic frame must be sufficiently bulky at its bridge and rim portions to hide or mask the underlying wire frame, and the front of the overlying plastic frame has enlarged bulk adjacent its temple portions to accommodate the separately formed hingeable latches.
This design relies on frictional engagement between the wire and plastic bridges which is susceptible to wear over years of use. To compensate for this wear, the temple pieces can be adjusted to increase pressure on the wearer's ear, thereby pressing the bridge portions together, but this may be uncomfortable over extended wearing times.